1. Field of the Invention
The present invention relates to vehicular semi-automated mechanical transmission systems of the type responding to a manually or automatically selected shift from a currently engaged gear ratio into a target gear ratio by automatically biasing the transmission to be shifted from the currently engaged gear into neutral and thereafter requiting a manual intervention to cause a drive train torque break to allow the shift into neutral to occur, and, in particular, relates to a control system/method for the above-described type of semi-automated mechanical transmission system which will, until a shift into neutral is confirmed, repetitively prompt the vehicle operator to manually cause a torque break.
2. Description of the Prior Art
Vehicular partially automated mechanical transmission systems wherein automatically or manually selected shifts of the mechanical transmission are semi-automatically implemented in a system having a manually only controlled engine throttle means and a manually only controlled master clutch are known in the prior an as may be seen by reference to U.S. Pat. Nos. 5,053,961 and 5,053,962, both assigned to the assignee of this invention, Eaton Corporation, and the disclosures of both of which are incorporated herein by reference.
The partially automatic shift implementation systems, which do not require automatically controlled throttle or clutch actuators, preferably have at least one mode of operation wherein the shifts to be semi-automatically implemented are automatically preselected. The systems include an electronic control unit (ECU) which, in the automatic preselect mode is effective for receiving input signals indicative of transmission input and output shaft speeds and for processing same in accordance with predetermined logic rules to determine if an upshift or downshift from the currently engaged ratio is required and to issue command output signals to a transmission actuator for shifting the transmission in accordance with the command output signals.
Upon automatic or manual selection of a shift from a current gear ratio into a target gear ratio, the control unit would automatically preselect a shift from the current gear into neutral by biasing the shift actuators to disengage the jaw clutch associated with the currently engaged ratio. However, as is well known, due to "torque lock", engaged jaw clutch members will not disengage until a drive train "torque break" or torque reversal is caused. Due to the lack of throttle and master clutch automated actuators, the vehicle operator is usually required to manually cause a non-torque lock condition by manipulation of the throttle pedal and/or momentary disengagement of the master clutch.
In the prior art systems, upon initiation of a shift from a currently engaged gear ratio, the operator is prompted or alerted, usually audibly by a single tone, that a shift has been selected. If the drive misses the tone, or forgets the warning, the driver may be unaware that the transmission is preselected toward neutral which may result in additional wear of the shift forks, shifting mechanism and/or electronic shift control unit due to extended preselect times.